Saunders and his students have broached the idea that selenium and tellurium freely substitute for each other in the mineralizing fluids that form low-S precious metal deposits. Following this insight, DIR applied its low-S production function derived from high grade gold-silver deposits in Arizona, Nevada, and Washington State, to the almost 50 year-old high density rock chip analyses obtained in the Cripple Creek mining district of Colorado by the US Geological Survey. The two maps below show the results from Cripple Creek. The same production function applied to much more modern US Geological Survey stream sediment geochemical data revealed eight other 'Cripple Creek style' low-sulfidation mining district-sized mineralized areas in central Colorado. Four of these are apparently under-developed brownsfield mining districts, while the other four are greensfield target areas.
Since mineral exploration money is very scarce, DIR's going to be confining its own exploration work to its backyard Colorado for the time being. Its Washington and Nevada gold exploration projects are being put on hold. Busy inspecting Central Colorado Assessment Project data from the USGS right now, since preliminary office orientation work show DIR's low-S epithermal selenium and/or telluride-containing precious metal translog production function is applicable to much of the state.
Summer and fall 2015 field and lab work on Nevada Carlin-type gold deposits produced a third iteration translog production function accounting for 98% of the variation in log10 Carlin-type gold deposit resource ounces contained in the subsurface of sampled drainage cells. Regressed geochemical data remain the NURE program drainage sediment geochemical re-analyses (10,000+ samples) found at http://pubs.usgs.gov/of/2000/of00-421/ . The Figure provided below illustrates the predictive power of the particular gold resource production function/algorithm in question.
What is remarkable is that, of the 310 drainage samples determined to be anomalous for Carlin-type gold mineralization in north central Nevada using the most recent iteration of the Carlin-type gold deposit production function, only 26% of these were not already staked; i.e., only 26% are on open ground. Judging by the NURE sample re-analyses, the historical reconnaissance stage exploration work of Nevada mineral exploration geologists has therefore been exceedingly effective in identifying ground prospective for Carlin-type gold mineralization. What is also surprising, though, is that only about 45% of the staked drainage sediment anomalies have so far been successfully explored to the extent that mines have been developed on them. Maybe what’s needed on the remaining 55% of the identified anomalies on existing claim holdings is more persistence and concentration: that’s what the geochemical data suggest, in any case.
Using its Carlin-type gold deposit geochemical production function derived from Carlin-type mineralization occurrences in the public domain NURE/USGS stream sediment sample 10,000+ drainage cell data set, DIR identified 27 high-priority Carlin-type gold prospect areas in the north central area of Nevada. Most of October was used to conduct follow-up stream sediment sampling of 15 of these target areas.
This follow-up sampling was carried out in order to:
1. Confirm the results of the NURE sampling and USGS chemical re-analyses of the NURE samples. On rare occasion on other projects, DIR has found the NURE era sampling work to be marred by sample mis-labelling and/or map location errors. (The NURE sampling work took place before the mapping convenience and relative accuracy of satellite GPS.)
2. Fill in gaps in the NURE stream sediment sample coverage. The Carter administration’s NURE program sampling was intended as reconnaissance-stage work only. Consequently, there are large areas of rock in Nevada (and elsewhere in the US) not represented in the NURE sampling coverage, and it is therefore usually not possible to fully define the extent of mineralization-related geochemical alteration surrounding NURE anomalies using first-pass NURE stream sediment sampling data only.
3. More closely define the rock source of geochemical anomalies discerned in the NURE/USGS data set. Some of the drainage cells sampled in the NURE program are as large as 15 square miles. Without follow-up subsampling, it is not possible to locate the specific rock area generating the mineralization-related geochemical anomaly.
Interestingly, this October follow-up sampling work provided some early encouragement concerning DIR’s exploration innovation. For example, the first project area sampled was, according to Nevada geological map coverage, supposed to be located in a large felsic intrusive body. Instead, as would be expected by the particular nature of the NURE geochemistry for that area, this anomalous drainage was found to be underlain by a strongly carbonaceous silty limestone, a limestone like those very frequently associated with Carlin-type gold deposits.
Also encouraging was the finding that two other NURE anomalies sampled during the month were located in long- to recently-abandoned mineral prospects marked by drill roads and drill pads. The younger of these two unstaked mineral prospects showed recent evidence of detail-scale geophysical and/or geochemical surface surveying (i.e., fresh survey line flagging).
Finally, it turned out that the geochemical data obtained from summer 2015’s sampling of drainage cells containing Carlin-type gold deposits that were missing from the NURE/USGS north central Nevada sample set are incompatible with the original NURE/USGS geochemical analyses. This problem is believed to be the result of basic differences in sample prep, sample digestion, and sample analysis procedure differences existing among the various labs involved. Fortunately, as shown in the two graphs below, each data set is internally consistent and permits statistical estimation of Carlin-type geochemical data production functions permitting close (90% adjusted r-squared) gold resource interpretation of Nevada stream sediment data. The NURE/USGS geochemical data production function for Carlin-type was, as first mentioned, used by DIR to filter the 10,000+ stream sediment samples for likely locations of undiscovered economically-mineralized Carlin-type gold deposits. On the other hand, the Carlin-type gold deposit production function, derived from summer 2015 sampling by DIR and analyses by ACME/BV Labs, will be used to interpret the geochemical data from DIR follow-up and infill stream sediment sampling work.
In July, DIR spent a couple weeks in Nevada, sediment sampling drainages containing known Carlin type gold deposits. Reasons for doing this work are two-fold:
DIR was able to gain access to and sample about 50 additional drainage cells containing Carlin gold deposits with known production and/or gold reserves during this July field work. Geologically, it was striking how each and every surface-exposed deposit visited evidenced large volumes of very strongly carbonaceous siltstone and/or limestone in the mine workings. Curiously, not all that much is said about this consistent Carlin type deposit characteristic in the economic geology literature.
One of the mining districts visited during July was the Jerritt Canyon/Independence Mountains Carlin type gold district of northern Nevada. The picture below the text provided here shows the current density of unreclaimed drill roads and mine workings in the Jerritt mining district. This sort of thing happens when discovered mines are not all that productive and profitable, and when the means of finding them isn't very discriminating. From ground level, the unreclaimed drill road density is also very obvious.
The geochemical data from the July Nevada stream sediment sampling will be used to refine DIR's Carlin type gold deposit production function. The refined function will, in turn, be used to steer DIR's green and brownfields Carlin type gold prospect generation work in Nevada. This prospect generation work should begin by the last week or two of this month.
DIR follow-up sampling of the five greenfields/brownfields gold prospects generated by last year's stream sediment sampling in the Republic area of northeast Washington was abbreviated in late August after about 50% of the follow-up work had been completed. Active forest fires there (temporarily) closed down road and other access to nearly all prospective land there. DIR plans to return to Washington next spring -- while things are still green and wet -- in order to finish the follow-up sampling needed.
The Boston Consulting Group recently (6/29/15) released a report analyzing the state of affairs in worldwide mineral exploration. The report can be found here: https://www.bcgperspectives.com/content/articles/metals-mining-tackling-crisis-mineral-exploration/.
There are two things that are striking about the report. First, nearly all of the recommendations proposed as means for reversing the declining annual mineral deposit discovery rate (and the declining discovery rate of the most valuable Tier 1 deposits, especially), have been held to be true within much of the mineral exploration industry for decades. (See, for example, Siegfried Muessig's short paper, "The Orefinders", first published in the SEG Newsletter in the late 1990s.) Perhaps the apparent inefficacy of these old internal views on the modern work of mineral exploration comes from upper management's deafness to them, or perhaps it comes from these views no longer being sufficient and adequate means -- given the gradual exhaustion of the easier to find low-hanging fruit -- for discovering economically-significant ore deposits. It's very probably a combination of these two possible explanations.
The second "striking" point could be causally related to the first in that the recommendations provided in the Boston Consulting Group report are largely a repetition of older, long-crystallized views. The report does not explore the possible effect of an aging mineral exploration work force on the mineral exploration crisis. Employment conditions in the industry have been in decline since the 1980s, so young geologists have been less and less motivated to enter and remain in the profession. With the consequently increasing average age of mineral exploration professionals, it seems likely that average problem-solving abilities have been gradually changing within the industry. With aging, the normal tendency is for fluid intelligence to decline and for crystallized intelligence to become more dominant. Fluid intelligence is that used to address novel problems like those constantly encountered in mineral exploration. In older people, traditional ways of approaching problems (crystallized intelligence) are maintained while problems that have not been previously encountered take them much extra time to figure out. See, for more discussion, "Cognitive skills and normal aging" at http://alzheimers.emory.edu/healthy_aging/cognitive-skills-normal-aging.html and the comparison of fluid and crystallized intelligence provided at https://en.wikipedia.org/wiki/Fluid_and_crystallized_intelligence. Perhaps at least some portion of the declining annual ore deposit discovery rate of the last decade or so reflects what time is doing to the average mineral exploration geologist because more youthful brains are justifiably shying away from the profession.
China has been the latest primary driver of the increased demand for commodities, as it's been intensely growing its hard-goods infrastructure. (Last time such a long interval of growth in global demand for metals, etc., corresponded to WWII, post-WWII reconstruction, and the eventual outfitting of baby boomer households.) China's demand for commodities has been gradually decreasing since 2007, evidently because the rest of the world's industrial economies are ebbing. This latest hiccup in China seems to me to be just another step in the worldwide, and the China-local, continuing economic decelerations.
As to this latest downward change in gold price level, see http://www.statista.com/statistics/299638/gold-consumer-demand-by-top-consuming-country/ The global "market" is apparently now betting that the recent stock market losers in China aren't going to increase or maintain their historical high rate of gold purchases any time soon.
In mining, what this all means is that companies that hope to survive and thrive are going to have to do it on the basis of increasing their production margins, not by continuing to rely on market-driven (China-driven) high price levels. This situation represents a huge stress to the whole mining industry because nearly all (see Goldcorp as one exception) have made their way lately by 'pigging it up' on the basis of China's increase of the global demand for minerals and the consequently heightened metals price levels. This has translated, in most metals, to the mining of increasingly low-grade ore material. (These are simple, very large exploration targets, locatable by the relatively unreflecting blitzkrieg exploration drilling approach favored by very many.) This, in turn, has led to a much smaller emphasis on the more difficult mineral exploration for smaller, higher grade, higher margin ore deposits, and an increase in the perceived internal importance of financial and mining engineering staff (rather than exploration staff). So, in the long run, the meltdown of global mineral demand spells very good news for the now almost vestigial business of mineral exploration:
Achieving higher margin metals production is going to eventually increase the importance of exploration work.
(I should live so long.)
Larry Turner is a mineral exploration geologist with a bias for exploration geochemistry. He started his professional work at the 1980 beginning of the just ended long-term cycle of growth in world-wide mineral exploration activity. He's dabbled in mineral economics, having gone through the Colorado School of Mines' Masters level program in this subject.